Tired, headaches, dizzy on Mounjaro or Wegovy – what’s behind it?

The manufacturers’ prescribing information (SmPC) explicitly lists these symptoms. “Common” there means: at least 1 in 100 people treated is affected.

The symptoms often appear in the first weeks and after a dose increase, and then get weaker for many people. You can find an overview of all other side effects in Mounjaro side effects.

The medicine itself is rarely the only reason. Usually it is a combination of these points:

• Too little energy: GLP-1 medicines strongly suppress hunger. If you accidentally eat only a few hundred calories a day, you feel drained and unfocused.
• Too little fluid: Less food also means less water from food, and thirst is often dampened. Nausea, vomiting or diarrhoea make this worse. According to the prescribing information, fluid loss can worsen kidney function, up to acute kidney failure.
• Electrolytes: With little food, you also take in less salt and fewer minerals. This can contribute to headaches and dizziness.
• Low blood sugar: On its own the risk is low. If you also take insulin or sulfonylureas, the risk is clearly higher according to the prescribing information – then the doctor often adjusts the other diabetes medicines.
• Blood pressure falls: Losing weight lowers blood pressure. That is good, but it can become too much – see the next section.

Many people with overweight take blood pressure medication, such as candesartan, ramipril or amlodipine. The dose was set for your old weight. When you lose weight with Mounjaro or Wegovy, your blood pressure often falls by itself. Then your usual tablet can suddenly be too strong.

Typical signs are dizziness when standing up, your vision “going black”, tiredness and a feeling of pressure in the head. Too little fluid makes the effect even stronger.

• Measure your blood pressure regularly at home during this phase, ideally morning and evening, and note the values, for example in the Tracker.
• Take the values to your GP. They decide whether the dose needs to be adjusted.
• Never stop or reduce blood pressure medication on your own.

More on combinations with other medicines in Interactions of the weight-loss injection.

Before you blame the injection, it is worth taking an honest look at the last two or three days. These questions help narrow down the cause:

1. How much have you really eaten? Write everything down for a day. Many people are surprised how little it has become on GLP-1 – especially protein.
2. How much have you drunk? Dark urine, a dry mouth and headaches in the afternoon point to too little fluid.
3. When does it happen? Dizziness right when standing up points more to blood pressure. Shaking, sweating and sudden intense hunger point more to low blood sugar.
4. Is it linked to your injection day? Many notice it most in the first one to three days after the injection, especially after a dose increase.
5. How are you sleeping? Poor sleep, stress or heartburn at night make you just as tired during the day. Tips on reflux can be found in Heartburn on the weight-loss injection.

If you note your answers along with weight, blood pressure and symptoms, you will have a good basis for your next doctor’s appointment. Important: don’t increase the dose faster on your own just because the symptoms have eased. The dosing schedule is set by your doctor – more in Mounjaro dosage.

• Drink regularly, even without feeling thirsty – spread across the day. How much makes sense is covered in How much to drink on the weight-loss injection?
• Don’t eat too little: several small meals with enough protein are better than one large one. Ideas can be found in Nutrition on the weight-loss injection.
• Keep an eye on electrolytes: With diarrhoea or vomiting, an electrolyte solution from the pharmacy can be useful. If you take ACE inhibitors or sartans such as candesartan, check with your doctor before taking extra potassium supplements, because these medicines can raise potassium levels.
• Magnesium: Whether and when it makes sense is explained in Magnesium and GLP-1. With kidney disease, only after consulting your doctor.
• Stand up slowly, especially in the morning and after sitting.
• Sleep and exercise: Light exercise in the fresh air helps many people against the slump; hard workouts on very little food tend not to.

For headaches, many people reach for over-the-counter painkillers from the pharmacy. Ask there briefly what fits with your other medicines – some painkillers put extra strain on the kidneys when you are short of fluid.

You should see a doctor soon if the symptoms do not improve after several weeks, you can barely eat or drink anything, or your blood pressure readings are clearly lower than usual. A blood test can also reveal other causes such as anaemia, thyroid problems or nutrient deficiencies. This article does not replace medical advice.